Vast floating islands of plastic are just a drop in the ocean compared with what’s lurking deeper down. Between 5 and 13 million tonnes of plastic debris entered the marine environment in 2010 – and most of it is under water. What’s more, without improvements in the way we manage waste, it could be 10 times as much each year by 2025.
It has been 40 years since the first scientific reports of plastic pollution in the ocean, but we still have plenty to learn. For instance, the combined results from 24 oceanic expeditions published late last year concluded there may beperhaps 244,000 tonnes of floating plastic out there. This is puzzling, because conservative estimates suggest something like 9 million tonnes of plastic have entered the oceans since the 1970s.
Now we know there’s even more missing plastic than that. Jenna Jambeck at the University of Georgia, Athens, and her colleagues have looked at data on plastic use and disposal in 192 coastal countries. They calculate that between 4.8 and 12.7 million tonnes entered the world’s oceans in 2010 alone. This means the amount of plastic that has entered the ocean down the years might be 1000 times more than the mass of floating plastic that scientific surveys have measured.
Surprisingly, the 10 countries with the largest problem – many of which are in south-east Asia – generally have relatively low rates of plastic waste generation per person. For instance, in China – which tops the list with an estimate of up to 3.53 million tonnes of plastic marine debris a year – the average person generates about 1.1 kilograms of waste per day of which just 11 per cent is plastic. In the US – at 20 on the list – the average person generates more than twice as much waste. But the top offending countries also have high coastal populations and low rates of plastic recycling.
It’s an interesting study, says Marcus Eriksen of the Five Gyres Institute in Los Angeles, who led last year’s floating plastic study
– but some of the assumptions used to arrive at the new calculations could be quibbled with. “I believe the authors underestimate the amount of trash that is scavenged, burned and buried before it reaches the ocean,” he says. “I think there’s much less leaving land.”
Even so, there is clearly a huge mismatch between the plastic entering the ocean and the plastic we find there. “The disturbing conclusion is that much of the plastic entering the oceans is unaccounted for,” says Carlos Duarte at the King Abdullah University of Science and Technology in Saudi Arabia, who has also helped conduct surveys into the amount of plastic in the oceans.
Where is the missing plastic? Perhaps it’s hiding in plain sight. “It’s important to understand that plastic shreds rapidly into microplastics that distribute widely into the most remote waters on the planet,” says Eriksen. “Of the 5.25 trillion particles of plastic we reported recently in PLoS One, 92 per cent are less than the size of a grain of rice.”
Such small particles spread throughout the water column, says Eriksen, also finding their way into sea-floor sediments and ice cores. That means we should stop thinking of plastic waste in terms of unsightly chunks of debris floating in vast oceanic garbage patches, and instead see it more as a pervasive “plastic smog” of tiny particles spread through the entire volume of ocean water.
“It’s not sensible to go to the ocean with nets to capture trash, but rather to focus on mitigation strategies on land,” says Eriksen.
Yet the amount of plastic entering the ocean is likely to keep rising in the years to come. Jambeck and her colleagues point out that 16 of the top 20 plastic producers they identified are middle-income countries, where strong economic growth will probably result in even more plastic use, but where the infrastructure to deal with the waste is still lacking.
But the solution isn’t to burden these developing countries with the cost of building effective waste management infrastructures, says Eriksen. Instead, we should require the plastics industry to rethink the way it designs its products – in particular, the industry should phase out plastic products designed for single use.
Change the way plastic is produced, says Eriksen, “and the plastic pollution issue would largely diminish”.